The micro accelerometer is an element widely applied to, for example, smart phones, wearable devices and Internet of Things (IOT) devices. The micro accelerometer may also be applied to other fields of engineering, science, and industry. For providing a function of displacement measurement on a modern application, the micro accelerometer has to be highly integrated, have low power consumption, and provide correct measurement in displacement.
Since most of the known micro accelerometers are manufactured by an MEMS or CMOS process with a very small size, they can only provide single direction magnetism measurement. In other words, some micro accelerometers use a single mass block to provide measurement of displacement in one direction (the Y direction) in the plane of the mass block and a direction (the Z direction) perpendicular to the plane. If measurement of displacement in all three directions is necessary, an additional detector that detects displacement of another mass block in a third direction (the X direction) will be needed. Some other designs use a single mass block to provide measurement of displacement in all three directions. The accelerometer so designed, however, is bulky and complicated, difficult to fabricate.
U.S. Pat. No. 7,757,555 B2 disclosed a three-axis accelerometer that includes one single mass block and two groups of detection electrodes, arranged at two perpendicular axes in the plane of the mass block. The two groups of detection electrodes do not only provide measure of displacement of the mass block in the two axial directions (X/Y) but also displacement in the vertical axis (Z direction). The accelerometer so disclosed is complicated in structure and difficult to fabricate.
CN 101133332B disclosed a three-axis two accelerometer that includes micro accelerometers, wherein one accelerometer measures the X direction and Z direction displacement of the mass block and the other measures the Y direction and Z direction displacement of the mass block. This micro accelerometer is bulky and its mass block and electrodes are complicated in structure and difficult to fabricate.
US 2011/0101008 A1 disclosed a three-axis micro accelerometer that includes one single mass block and two groups of moveable electrodes that detect displacement of the mass block in two perpendicular directions. The mass block and detection electrodes of this design are complicated in structure and difficult to fabricate. In addition, the micro accelerometer is bulky.
U.S. Pat. No. 8,413,511 B2 disclosed a three-axis micro accelerometer with two mass blocks. One mass block is accommodated within another mass block and the two mass blocks respectively provide measurement of displacement in the X/Y and the Z directions. Again, the accelerometer is bulky and its mass block is complicated in structure and difficult to fabricate.
WO 2012172528A1 disclosed a three-axis polymer micro accelerometer that includes a sealed chamber consisted of injected elements that heat the air enclosed in the chamber. When an external force is applied, a temperature gradient is generated. A detector detects the temperature and the results are used to calculate accelerations in three axes.
U.S. Pat. No. 8,459,114 B2 discloses a multiple axes micro accelerometer that includes two mass blocks. One mass block performs seesaw movement to provide measurement of displacement in the Z direction, while the other is suspended by springs to provide measurement of displacement in the X/Y directions. The accelerometer is bulky and its mass blocks are complicated in structure and difficult to fabricate.
At present, a novel structure of micro three-axis micro accelerometer is needed in the industry to provide detection of displacement in three axes.
Meanwhile, a novel micro three-axis micro accelerometer is also needed to provide detection of displacement in three axes using one single mass block.
Meanwhile, it is also necessary to provide a micro accelerometer capable of integrating a three-axis displacement measurement function in a single mass block by taking the advantages of the standard CMOS process.
It is also necessary to provide a three-axis micro accelerometer that is simple in structure and easy to fabricate.